Electric arc furnace for continuously melting scrap iron

ABSTRACT

A method for continuously melting metallic products, especially scrap iron, in an electric arc furnace and a furnace for carrying out the method, in which the products to be molten are fed into the furnace hearth through a compartment which communicates at its lower end with a lower portion of the hearth and which is separated by a refractory wall from the upper hearth portion so that the products while being fed are protected from the heat produced by the electric arcs and fusion of the products during feeding thereof is prevented.

United States Patent Dumont-Fillon et al.

[ 51 May 23, 1972 [54] ELECTRIC ARC FURNACE FOR CONTINUOUSLY MELTINGSCRAP IRON [72] Inventors: Jacques Dumont-Fillon; Charles Roederer,

both of Metz (Moselle), France [73] Assignee: Institut De Recherches DeLa Siderurgie Francaise, St. Germain en Laye, France [22] Filed: July25, 1969 [21] App1.No.: 844,787

[30] Foreign Application Priority Data July 31, 1968 France ..161243[52] US. Cl. ..13/9, 13/34, 75/11 [51] Int. Cl. ..H05b 7/18, 0210 5/52[58] Field of Search ..75/11, 10; 13/9, 34; 266/27, 266/5 C; 263/27;214/182 [56] References Cited UNITED STATES PATENTS 3,249,423 5/1966Stewart... ..75/11 3,472,650 10/1969 Sibakin ..75/11 3,441,651 4/ 1 969Viens 13/9 2,011,288 8/1935 Kemmer ..75/11 2,776,881 l/1957 Thomsen......75/11 2,978,315 4/1961 Schenck ...75/11 3,167,420 1/1965 Robiette...75/l1 3,372,223 3/1968 Menegoz ..13/9 3,379,816 4/1968 HOZven......13/9 3,396,954 8/1968 Kirogsrud... ..13/9 3,461,214 8/1969 Schlienger..13/9 3,463,629 8/1969 Hatch ..75/1 1 Primary ExaminerWinston A.Douglas Assistant Examiner-Peter D. Rosenberg Attorney-Michael S.Striker [5 7] ABSTRACT A method for continuously melting metallicproducts, especially scrap iron, in an electric arc furnace and afurnace for carrying out the method, in which the products to be moltenare fed into the furnace hearth through a compartment which communicatesat its lower end with a lower portion of the hearth and which isseparated by a refractory wall from the upper hearth portion so that theproducts while being fed are protected from the heat produced by theelectric arcs and fusion of the products during feeding thereof isprevented.

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ELECTRIC ARC FURNACE FOR CONTINUOUSLY MELTING SCRAP IRON BACKGROUND OFTHE INVENTION The present invention relates to a method for continuouslymelting scrap iron in an electric arc furnace as well as in a furnacefor carrying out the method.

The melting of scrap iron in an electric arc furnace has so far alwaysbeen carried out in a discontinued manner, since the charge for thefurnace is supplied to the latter in successive portions, each of whichcan be introduced into the furnace only after the proceeding portion hasbeen molten. The drawbacks of such process are well known in the art andthey include the loss of time during the various charging operations,electric power fluctuations during collapse of the freshly-fed scrapiron at the melting thereof in the furnace, the danger of breaking theelectrodes, a reduction of the thermal output, and increased wear of thelining of the furnace.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide for a method and apparatus for continuously melting scrap ironto thus overcome the disadvantages of methods and apparatus known in theart.

In the apparatus according to the present invention, the products to bemolten have to arrive continuously at the melting zone, withoutnecessarily requiring a continuous charge of the material to be molten.The arrangement has to be made in such a manner that a progressiveheating of the scrap iron during the feeding thereof into the hearth ofthe furnace is avoided, to thereby prevent softening of the materialwhich would cause the srap iron pieces to stick together and therebyprevent, or at least render more difficult, further feeding thereof.

With these objects in view, the method according to the presentinvention for continuously melting metallic products, especially scrapiron, in an electric arc furnace, mainly comprises the steps of meltingthe products in the lower portion of the hearth of the furnace byelectric arcs, feeding new products to be molten from above andlaterally from the hearth into the lower portion of the latter so thatthe products form at the lower hearth portion a descending slope incontact with the molten material while protecting the products in theupper portion of the furnace from the heat developed by the electricarcs so as to prevent fusion of the products during the feeding thereofinto the lower hearth portion, and discharging the molten material fromthe lower hearth portion of the furnace.

The method according to the present invention may also include incombination with the above-mentioned steps, the step of regulating thespeed of melting of the metal by regulating the electric power furnishedto the electrodes of the furnace.

It is also an object of the present invention to provide for an electricarc furnace for carrying out the above method and the furnace, accordingto the present invention, mainly comprises wall means forming a hearthof the furnace, electrode means extending downwardly into the furnace,and having lower ends above the bath of molten material forming at thelower portion of the hearth, means for feeding metallic products to bemolten into the lower hearth portion and comprising at least onecompartment adjacent the hearth, separated from the upper part of thehearth by a substantially vertical wall of refractory material andcommunicating at the lower end thereof with said hearth, and meanscommunicating with the lower portion of the hearth for dischargingmolten products therefrom.

The furnace, according to the present invention, may also have thefollowing characteristics in combination with the characteristicsmentioned above:

a. the furnace may have a substantially circular cross section and thementioned at least one compartment may be ring-shaped;

b. the furnace may have a rectangular cross section and comprise twocompartments located at opposite sides of the longitudinal axis of thefurnace hearth;

c. the mentioned refractory wall may be provided with means forcirculating a cooling fluid therethrough; and

d. the electrodes in the furnace of rectangular cross section may bealigned with each other in a plane, which preferably coincides with thelongitudinal plane of symmetry of the rectangular furnace.

Basically, the present invention relates to a process and to anarrangement for carrying out the process in which the metallic productsintroduced into the electric arc furnace are protected during thefeeding thereof from the heat radiated by the electric arcs and to meltthese products in the lower zone of the furnace by means of the electricarcs. Metallic products thus introduced will remain at relatively lowtemperature until they are exposed to the heat developed by the electricarcs. To this effect a wall of refractory material separates the hearthof the furnace in which the electric arcs are produced, from acompartment into which the products to be molten are introduced. Thiswall extends from the top of the furnace to a distance which may varybetween a few centimeters and about hundred centimeters above themaximum level of the liquid bath of molten material forming at thebottom of the hearth so that in a lower zone of the furnace the hearthand the compartment communicate with each other. In this zone, themetallic products introduced into the compartment are thus suddenlyexposed to the heat developed by the arcs and melt rapidly. This rapidtransition from a low-temperature zone to a zone of melting will preventprolonged maintenance of the products to be fed in a region of elevatedtemperatures of between 900 and 1,200 C. in which a plastic deformationand resulting adherence to each other of the pieces to be fed wouldoccur, which could cause hanging of the charge, detrimental to theproper charging of the furnace.

In addition, the maintenance of the scrap iron at relatively lowtemperature until it reaches the zone of fusion permits also to avoidoxidation of the same which is harmful to the metallurgical as well asto the thermal balance of the operation. Thus, increase in theproductivity of the furnace is obtained. I

Furthermore, the presence of ferrous products along the outer wall ofthe furnace at the level of the metallic bath forms a protective shieldwhich will prevent rapid deterioration of the furnace lining at theportion thereof which is thus protected from the heat radiation producedby the arcs so that the useful life of the furnace is increased.

Finally, since a thermal equilibrium exists between the liquid phase andthe mass of solid material to be molten which are in contact with eachother, the melting speed of the material in the furnace will bedetermined by the electric power and not by the speed of charging thematerial into the furnace. Consequently, the manner of charging may becontinuous or discontinuous according to the type of products to bemolten.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a firstfurnace embodiment according to the present invention;

FIG. 2 is a cross section taken along the line A-B of the furnace shownin FIG. 1;

FIG. 3 is a plan view of a second embodiment of the furnace according tothe present invention;

FIG. 4 is a plan view of a third embodiment of the furnace according tothe present invention;

FIG. is a sectional view taken along the line C-D of the furnace shownin FIG. 4; and

FIG. 6 is a schematic plan view of a further embodiment similar to thatshown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 illustrate anelectric arc furnace 1 of substantially circular cross sectioncomprising a hearth 2 and a compartment 3 separated in the upper portionof the hearth 2 by a refractory wall or shield 4. The hearth 2 is formedby a cylindrical wall 5 of refractory material, a sole 6 and a vault orroof 7 likewise formed of refractory material. Three electrodes 8a,8b,and 80 extend through appropriate openings in the roof 7 insubstantially vertical direction into the hearth and the electrodes arerespectively supported on arms 9a,9b, and 9c which serve at the sametime to supply the electrodes with electric current in a manner known inthe art from transformers, not shown in the drawing. The hearth isfurther provided with a spout 10 for discharging the slag and with anopening 11 to discharge the molten metal from the lower hearth portionand such discharge from the opening 11 may be carried out by a siphonsystem of known construction.

The compartment 3 has thus a substantially annular form surrounding thehearth except for the zone in which the support arms are arranged andthe zone through which discharge of the molten products takes place. Itis also possible to arrange the spout 10 and the opening 11 in the zonein which the support arms are provided so that the compartment 3 may beextended and the surface of the wall 5 which is not protected bereduced. The compartment 3 is defined by an inner curved wall 4 whichabuts against the roof and an outer curved wall 12 and two straightwalls 13 and 14 which project only upwardly from the roof and which donot extend into the interior of the hearth 2. These walls thus form anannular hopper which projects upwardly essentially beyond the level ofthe roof 7 and which thus facilitates the charging operation. The wall12 forms a broken outline with an oblique portion 12a in the zone whichis not protected by the shield 4. The angle which the oblique portion12a includes with a horizontal is shown about 60. This slope has theadvantage to facilitate sliding of the products which are still solidand their discharge into the molten metal. The furnace described ispreferably used for melting scrap iron.

The charging of the scrap iron through the open end 15 of thecompartment or hopper 3 is preferably made by means of an electromagnetl6, suspended and operated from a gantry crane, not illustrated, andwhich permits to place the scrap iron at any point at the annular spaceof the hopper 3 and to supply in this way each portion of this hopper.On the other hand, the scrap iron may be directly discharged from scrapiron stock contained in a railroad car or truck, for example, whichconstitutes another advantage of the furnace according to the presentinvention.

During its descend in the hopper 3, the scrap iron is protected from theheat radiation from the electric arcs by the wall 4 which, as mentionedabove, is of refractory material and therefore a poor heat conductor.Nevertheless, during the operation of the furnace, the wall 4 is exposedto the heat radiation from the metallic bath at the bottom of the hearthand to a lesser degree also to the heat radiation from the electricarcs. To avoid deterioration of the wall 4 by excessive heating, thelatter is provided with an interior cooling space 17 into which coolingwater is fed through the conduits l8, and discharged through theconduits 19. It is to be understood that instead of cooling water alsocold air or another cooling fluid may be circulated through the passageswhich are provided in the wall 4. Due to the protective shield 4,whether it is cooled or not, the scrap iron will arrive at the bottom ofthe compartment 3 at a relatively low temperature which will definitelybe beneath the temperature at which the pieces of scrap iron soften andadhere to each other. Then, suddenly, the scrap iron will be exposed tothe heat radiation of the electric arcs and melt at the bottom of thehearth. However, the melting scrap iron will be immediately replaced bynew scrap iron in such a manner that at any instant there will exist aprotective shield which covers the lower portion of the wall 12 and inparticular the oblique portion 12a thereof. The wall 4 is constructed insuch a manner to form a passage 20 between the hearth 2 and thecompartment 3, a passage which permits formation of a slope of scrapiron moving downwardly towards the interior of the furnace in thedirection indicated by the arrows. This passage has, in the exampleillustrated, a height of about 50 centimeters above the maximum level Aof the bath of liquid metal at the bottom of the hearth and the form ofa circular slot. The wall 4 is extended beneath the roof 7 by wallportions 4a,4b which serve to guide the downwardly moving slope of scrapbeyond the extremities of the compartment 3. This has the advantage toform a protective shield of scrap iron along an important portion of thewall 5, and to avoid that the pile of scrap iron comes into contact withthe electrodes. In this way, a short-circuit with the scrap iron isavoided and a liquid bath is maintained which assures proper stabilityof the electric arcs, which in this case will form exclusively betweenthe electrodes and the liquid bath forming at the bottom of the hearth.At the same time, imparting of mechanical shocks to the electrodes byfalling scrap iron is avoided and the risk of breaking the electrodes isthus greatly diminished.

Another advantage according to the present invention is that it ispossible to constantly use the maximum power available while providingexcellent conditions for heat transmission since most of the heatradiation is received by the products to be molten.

Another advantage which results from the above is that regulation of thepower supply is greatly simplified, as compared with electric arcfurnaces according to the prior art, so that the electric arc furnaceaccording to the present invention is simpler in construction and moreeasily to maintain in proper condition than are furnaces known in theart.

Since a solid phase of the material to be molten is constantlymaintained in contact with the liquid phase, the temperature of theliquid phase is in the region of this contact, equal to the temperatureof the liquidus and the total electric power used in this zone serves tomelt the metal.

Another advantage of the present invention resides therefore in thepossibility to precisely control the speed of melting of the scrap iron,and consequently the output of the furnace, since in this case theoutput is a function of the electric power supplied which may beprecisely regulated.

In addition, the great flexibility of the means for charging the furnaceaccording to the present invention permits to introduce into the furnacescrap iron pieces which differ essentially from each other as todimensions and weight.

An additional advantage of the furnace according to the invention isthat the openings for discharging the molten products from the lowerhearth portion are arranged distant from the compartment 3, that is,from any scrap iron which is still solid. The temperature of the bathheated by the electric arc is therefore an elevated one in the region ofthese outlet openings, which greatly facilitates discharge of metal andslag.

During supply of electrodes from a three-phase network, the electrodesare, as known, not maintained exactly at the same tension, but one ofthe electrodes is charged to a higher degree than the other. This oneelectrode will evidently develop a more intense heat radiation than theothers, and for this reason, the one electrode, that is for instance theelectrode 8c, is placed, if possible, in such a manner that it issurrounded by the slope of scrap iron so that the surplus energy thusradiated from the electrode, is used for a maximum yield. Thetransmission of energy from the electrode may be improved, for instance,by the use of an electromagnetic mixer and the action of such a mixer,which is not represented in the drawing, permits also to facilitate theoutflow of the molten products and to prevent formation of a salamander,or a mass of solid material at the sole of the furnace.

FIG. 3 illustrates a further embodiment of a furnace according to thepresent invention. The furnace illustrated in FIG. 3 is likewise acircular furnace which includes elements corresponding to the elementsof the furnace illustrated in FIGS. 1 and 2 and described above and suchcommon elements are designated in FIG. 3 with the same referencenumerals to which however a prime is added. The furnace illustrated inFIG. 3 comprises two annular compartments or hoppers respectivelydesignated with 3' and 3" and located outside of the zone in which thesupport arms 9a,9b, and 9c are provided and in which the means 10 and 11for discharge of molten products from the furnace are located. Thecompartments 3 and 3 are respectively limited by the circular walls 4and 12, respectively 4" and 12", and by the straight walls 13 and 14',respectively 13 and 14". The straight walls extend only upwardly fromthe roof 7 of the furnace and do not penetrate into the interior of thehearth 2 thereof. The arrows in FIG. 3 indicate the direction in whichthe slopes of material forming at the bottom of the compartments willmove, and as can be seen from FIG. 3, such movement of the material willextend also beneath the support arms 9a,9b and 9c. In this zone of thesupporting arms, the downwardly extending slopes of the material comingfrom the compartments 3' and 3" may join each other due to the wallportions 4'a and 4"a which, beneath the roof 7, extend the walls 4 and4", whereas at the other extremity of the compartments 3 and 3", thewall portions 4'b and 4!) extend, beneath the roof 7, the walls 4' and 4so that only the channel for the discharge of slag and steel ismaintained free of solid scrap iron. This construction has the advantageto create a protective ring all around the wall of the furnace with theexception of the zone for discharge of the molten products. The moltenproducts are discharged in the modification illustrated in FIG. 3through the spouts l and 11 which are located side-by-side.

FIGS. 4 and illustrate a third embodiment of the furnace according tothe present invention, in which the furnace has a rectangular crosssection. In the modification illustrated in these two Figures, there areprovided two lateral compartments 3 and 3" of rectangular configurationlocated at opposite sides of the central hearth 2. An advantage of thisarrangement is that the two lateral compartments may be supplied withmaterial to be molten by transporting bands 21, one of which extendsbeneath at least one of the arms supporting and supplying current to theelectrodes. The means and 11 for discharging the molten products fromthe hearth are located at opposite ends of the hearth 2. In thismodification, the sole 6 of the hearth is slightly inclined from theslag discharging spout 10 toward the opening 11 serving to discharge themolten steel, which facilitates discharge of the molten metal from thefurnace. Furthermore, the electrodes 8a,8b, and 8c are aligned along acentral longitudinal plane of symmetry of the furnace.

Such a construction in which the hearth has a rectangular cross section,in which the electrodes are aligned along the longitudinal plane ofsymmetry of the hearth, and in which two downwardly moving slopes ofmaterial to be molten are provided, may also be used in furnacesdiffering from that shown in FIGS. 4 and 5, for instance in a furnaceillustrated in FIG. 6 in which six electrodes, that is the electrodes 8a8f are aligned along the longitudinal plane of symmetry of the hearth 2.These electrodes are connected to the secondary windings of thetransformer P, as schematically illustrated in FIG. 6.

While the charges for the furnace as described above have been describedas scrap iron of any origin, it is to be understood that the inventionis not limited in this respect, but that also other forms of metal forinstance classified scrap iron or pre-reduced products in the form ofpellets, sponge iron or briquettes, etc., may also be used.

Finally, the invention may be used for the discontinued production ofmolten metal with individual charges and rocking of the furnace aftereach operation, as well as for the uninterrupted production of steel bycontinuous melting of scrap iron in which the furnace constitutes themelting stage of a known process for treating metal. In the latter case,it is not necessary to provide for a rocking of the furnace.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofmethod and apparatus for melting metallic products.

While the invention has been illustrated and described as embodied in amethod and apparatus for continuously melting of scrap iron, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim:

1. A furnace for continuously melting scrap metal products, comprisingwall means forming a hearth of said furnace; electrode means extendingdownwardly into said furnace and having lower ends above the bath ofmolten material forming at the lower portion of the hearth; means forfeeding scrap metal to be molten into the lower hearth portion andcomprising at least one compartment adjacent a portion of the peripheryof said hearth;-a wall of refractory material located between saidcompartment and said hearth for shielding the scrap metal fed throughsaid compartment from the heat radiated by said electrode means, saidwall means having a lower end located slightly above the level of thebath in said hearth and at the region of the arcs formed between thelower ends of said electrode means and said bath so as to form betweensaid compartment and said hearth a passage located in the region of saidarcs for admission of scrap metal from said compartment in said hearthsubstantially at the level of the arcs, while the scrap metal descendingthrough said compartment is protected from said arcs by said wall ofrefractory material.

2. A furnace as defined in claim 1, and including means for supplyingelectrical energy to said electrode means; and means communicating withsaid lower hearth portion for discharging molten products therefrom,said at least one compartment extending about a major portion of theperiphery of said hearth spaced from said discharging means. 7

3. A furnace as defined in claim 2, wherein said at least onecompartment has an end spaced from the means for supplying electricalenergy to said electrode means.

4. A furnace as defined in claim 1, wherein said furnace has asubstantially circular cross section and wherein said at least onecompartment is substantially ring-shaped.

5. A furnace as defined in claim 1, wherein said furnace has arectangular cross section and comprises two compartments located atopposite sides of the longitudinal axis of the furnace hearth.

6. A furnace as defined in claim 1, and including means for cooling saidwall of refractory material and comprising conduit means embedded insaid wall for circulating a cooling fluid therethrough.

7. A furnace as defined in claim 5, wherein said electrodes are alignedwith each other in a plane.

8. A furnace as defined in claim 7, wherein said plane coincides withthe longitudinal plane of symmetry of said rectangular furnace.

9. A furnace as defined in claim 4, and including means for supportingand for supplying electrical energy to the upper ends of saidelectrodes, said at least one compartment being located laterally fromsaid supporting and supplying means.

10. A furnace as defined in claim 9, wherein said means for dischargingmolten material from said furnace are located substantiallydiametrically opposite said supporting and supplying means of saidelectrodes, and wherein said furnace includes two compartments locatedsubstantially opposite each other and respectively between saidsupporting and supplying means and said discharging means.

1. A furnace for continuously melting scrap metal products, comprisingwall means forming a hearth of said furnace; electrode means extendingdownwardly into said furnace and having lower ends above the bath ofmolten material forming at the lower portion of the hearth; means forfeeding scrap metal to be molten into the lower hearth portion andcomprising at least one compartment adjacent a portion of the peripheryof said hearth; a wall of refractory material located between saidcompartment and said hearth for shielding the scrap metal fed throughsaid compartment from the heat radiated by said electrode means, saidwall means having a lower end located slightly above the level of thebath in said hearth and at the region of the arcs formed between thelower ends of said electroDe means and said bath so as to form betweensaid compartment and said hearth a passage located in the region of saidarcs for admission of scrap metal from said compartment in said hearthsubstantially at the level of the arcs, while the scrap metal descendingthrough said compartment is protected from said arcs by said wall ofrefractory material.
 2. A furnace as defined in claim 1, and includingmeans for supplying electrical energy to said electrode means; and meanscommunicating with said lower hearth portion for discharging moltenproducts therefrom, said at least one compartment extending about amajor portion of the periphery of said hearth spaced from saiddischarging means.
 3. A furnace as defined in claim 2, wherein said atleast one compartment has an end spaced from the means for supplyingelectrical energy to said electrode means.
 4. A furnace as defined inclaim 1, wherein said furnace has a substantially circular cross sectionand wherein said at least one compartment is substantially ring-shaped.5. A furnace as defined in claim 1, wherein said furnace has arectangular cross section and comprises two compartments located atopposite sides of the longitudinal axis of the furnace hearth.
 6. Afurnace as defined in claim 1, and including means for cooling said wallof refractory material and comprising conduit means embedded in saidwall for circulating a cooling fluid therethrough.
 7. A furnace asdefined in claim 5, wherein said electrodes are aligned with each otherin a plane.
 8. A furnace as defined in claim 7, wherein said planecoincides with the longitudinal plane of symmetry of said rectangularfurnace.
 9. A furnace as defined in claim 4, and including means forsupporting and for supplying electrical energy to the upper ends of saidelectrodes, said at least one compartment being located laterally fromsaid supporting and supplying means.
 10. A furnace as defined in claim9, wherein said means for discharging molten material from said furnaceare located substantially diametrically opposite said supporting andsupplying means of said electrodes, and wherein said furnace includestwo compartments located substantially opposite each other andrespectively between said supporting and supplying means and saiddischarging means.